When stem cells divide, the two daughter cells have a choice. Commonly, one of the daughter cells becomes a new stem cell while the other one will be more specialized (or differentiated). This property -- the ability to generate more stem cells (self-renewal) while making differentiated cells simultaneously -- defines a stem cell. Stem cells have the unique ability to divide asymmetrically but how this happens is poorly understood. Moreover, there is little knowledge on the mechanisms by which external signals control asymmetric division of stem cells. In tissues, it is also essential that the orientation of stem cell division is properly regulated. At the most fundamental level, asymmetry and the orientation of cell division are at the heart of stem cell biology.
We have found that we can instruct stem cells to divide in an asymmetric way by applying an external signaling molecule (called Wnt) to stem cells in a spatially controlled way. We found that the proximal daughter cell will become another stem cell while the distal cell is differentiated. We propose to examine the organization of human stem cells as they divide asymmetrically. Using live imaging microscopy and other tools, we intend to follow how critical determinants segregate over the two daughter cells. We expect that the new mechanistic insights into asymmetric stem cell division will ultimately lead to a better understanding of the possible use of stem cells for therapy.

Statement of Benefit to California:

This research proposal aims at understanding asymmetric divisions of stem cells, a fundamental biological property. The research will initially increase our insights into the basic biology of stem cells. In the longer term however, this work will also lead to better methods to manipulate stem cells for therapeutic purposes, as it will be essential to understand the ways that stem cells divide and differentiate.
Our work will also lead to technological advances that will be of use to stem cell researchers and stem cell-based applications. In fact, we have already made several advances in designing methods to direct the growth of stem cells, including the use of artificial niches and the use of specific growth factors that influence stem cells.

Review Summary:

The goal of this proposal is to study the mechanism of asymmetric stem cell division, whereby a stem cell can divide to give rise to one daughter cell that is a new stem cell and another daughter cell that has a more specialized fate. The applicant has demonstrated that spatially localized exposure to an external signaling molecule (Wnt) can induce such asymmetric divisions. The applicant plans to study these Wnt-induced asymmetric divisions in human stem cells using specialized imaging techniques to examine the subcellular partitioning of various determinants of cell fate (Aim 1). In addition, the applicant will examine the requirement for known Wnt pathway and centrosomal components in asymmetric division (Aim 2) and will screen novel modulators of Wnt pathway activity for their role in both pluripotency and asymmetric divisions of human and mouse embryonic stem cells (hESC, mESC) (Aim 3).

Significance and Innovation
- Asymmetric cell division is an important topic in stem cell biology and the linkage between asymmetric divisions and signaling pathways is understudied in vertebrate stem cells.

- If successful, the results of these studies would be of interest to the entire stem cell community and may broadly impact other areas of cell biology.

- The approach of studying single cells dynamically as they undergo cell division is highly innovative.

Feasibility and Experimental Design
- Extensive preliminary data support the idea that Wnt can induce asymmetric cell division in mESC, although it has not yet been demonstrated whether Wnt has a similar effect on hESC.

- The use of Wnt-coated beads to create a polarized signal is a powerful approach that should provide meaningful information.

- The screening system will allow identification of both known and novel Wnt pathway modulators that affect asymmetric stem cell division.

Principal Investigator (PI) and Research Team
- The PI is a leader in his/her field and has a clear track record of success.

- The Partner PI is a well-chosen collaborator for the proposed screening work.

- The team is excellent, and both the PI and Partner PI have the necessary expertise to carry out the proposed work.

Responsiveness to the RFA
- The proposal is responsive to the RFA, provided the applicant successfully translates the findings and approaches from mESC to the study of human stem cells.